Directional aerial system



April 159 1941., J M FURNWAL TAL 2,238,107

DIRECTIONAL AERIAL SYSTEM FiledAug. 5l, 1958 I l I y i l "2' ,41 MQ Afyfp I i A f I. i A2 E ,la/VMI, I

Patentecl Apr. 15, 1941 Unirse. stares cargar ortica DIRECTIONAL AERIAL SYSTEM:

John Megarry Furnival, Purley, Bertram 'John Witt, Harrow, and Christopher Sydney Cockerell, Danbury, England, assigncrs to'Radio Corporation of America, a corporation of Delaware Application August 31, 1938, Serial No. 227,808 In Great Britain September 28, 1937 (c1. 25o-1i) 5 Claims.

In one well-known type of short wave equisignal beacon, radiated waves are concentrated into two overlapping beams by means of directive aerial arrays or beam aerial systems. It is of great importance that the radiation from these arrays or aerial systems shall be as free as possible from spurious polarization away from the plane in which it is intended that the radiation i the system shall be polarized. Thus, if, in a system in which the radiation is intended to be polarized vertically, there be a horizontal com- 'I ponent in the transmitted radiation, and if, moreover, there is a horizontal component inherent in a cooperating mobile receiver (e. g., an aircraft receiver) which is making use of the beacon, errors, which will vary in extent both with the amount of horizontal component and with the inherent component of the particular mobile receiver, will occur. Thus, for example, if the equisignal course, i. e., the predetermined guiding line, is in a west-east direction, and if a cooperating mobile receiver is approaching this course in a general north-south direction, the point at which the receiver will obtain the two differently 'characterized elds at equal strength will not be A the same as that at which the said receiver would obtain the same result if it were approaching the course from the south-north direction. This discrepancy arises from the fact that in the iirst case the tilt given to one of the beams by the horizontal component to the wave front will assist the horizontal component of the mobile receiver whilst the tilt given to the wave front of thel other beam will oppose that of the receiver. In the second case, the receiving aerial system being now turned through 180, these effects will be reversed. The resulting error of observation may beextremely harmful to accurate navigation. Other forms of error may also be present.

The object of the present invention is to overcome the above defect, and this object is achieved according to the invention by so arranging matters that no horizontal component is present in the wave iront proceeding along the equisignal line. In other directions there may be present some horizontal component without being detrimental to the performance of the system.

The invention is illustrated in and further explained in connection with the accompanying schematic drawing, in which Figure 1 is a diagram of a known aerial system; Figure 2 is a diagram representing an embodiment of this invention; Figure 3 is a modified form using three directional aerials; and Figure 4 is an embodiment in which the phase of one aerial of each array is displaced.l

The accompanying Figure l shows diagrammatically a known short wave radio beacon comprising two series phase aerials of the type described and claimed in Patent No. 2,053,658, issued to C. S. Franklin, September 8, 193-5. The aerial consists of a series of quarter wave loops spaced a quarter wave apart. The quarter wave loops are vertically positioned, and, due to the current distribution, the loops are equivalent to a series oi vertical quarter wave aerials fed in phase quadrature. The radiations from the loops add in one direction and cancel in the opposite direction, so that the axis of maximum radiation is in the direction f-a. Due to the current relationships in the horizontal quarter wave portions of the array and the fact that they have length in the horizontal plane, radiation from the horizontal wires is negligible in the direction of the axis of maximum radiation, lbut is somewhat greater in directions at an angle thereto, that is, along the desired equi-signal course E. A more complete discussion of the" fundamental principles of 'the series phase antenna is found in Short Wave Wireless Communication by Ladner and Stoner, third edition, at page 306, et seq.

Two such arrays are. generally designated A and A and fed from a transmitter T via feeders F and F'. These aerials, each of which has horizontal portions a-b, c--d, e-f, or awb, c-d, e-f', respectively, are arranged opposite one another one on each side of theI desired equisignal line, which is represented by the chain line E, the said aerials being arranged at equal acute angles to the line E, which accordingly bisects the angle between the two said aerials, in order that the. required two overlapping directional polar radiation diagrams resulting in the equisignal line E may be obtained. Now with an arrangement as shown in Figure l, radiations of course occur from the horizontal portions al-Zr, 1V-b', c-d, c'-d', e-f, e'-f, and although, theoretically, these radiations should lcancel one another out at la distance, in practice there is always an unso that a line joining the front vertical portions of two adjacent arrays makes. an angle other than a right angle with the equisignal-line.

Figure 2 shows diagrammatically one embodiment of the invention. Like reference characters in Figs. 1 and 2 have like signicance. v In Fig. 2v

there are two series phase aerial arrays AI, A2, Al A2', each side of the equisignal line and symmetrically arranged. The aerial arrays are parallel to the equisignal line E, and, as will be seen, the arrays Al, AI are set back with reference to the arrays A2, A2 so that the lines X-Y joining the front vertical portions of the aerials AI, A2 and AI A2 are not normal to the line E. The arrow headed lines P--Q represent respectively the directions or Aaxes of maximum radiation from the systems AI A2 and AI A2 respectively; thus, in a dot-dash equisignal beacon, P might be the direction or axis of maximum radiation of the dotcharacterized eld and Q that of the dash-characterized iield.

In a further modification illustrated in Fig. 3 an aerial system consisting of three parallel arrays Al', A and AI (parallel to the equisignal H line) are used, power being continuously applied to the centre array A and alternately by a key K in dot-dash sequence to the two outer arrays.v Slewing of the beams is effected by setting back the two outer arrays so that lines X, Y joining the front verticals of the centre A and thel outer Al, AI arrays for an angle other than a right angle with the equisignal line E.

A similar effect may be produced by the use of two directly fed parallel aerials slewing of the beams, in this case, being effected by suitable phase adjustment, as shown in Fig. 4; Suitable phasing networks P are included in the lead to one aerial oi each array. Setting one aerial back is not necessary in this case.

The invention is not limited to the use of any particular form of aerial nor to the use of any particular nature of field characterization but is of general application to equisignal radio beacons.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. An equi-signal radio beacon aerial system comprising a plurality of directional aerials positioned on either side of the equi-signal line and having axes of maximum radiation parallel to said line, means for energizing said aerials, one of said plurality of directional aerials on each side of said line being set back with respect to the other aerials to produce a resultant radiation pattern on each side of said line having an axis of maximum radiation which is divergent from said equisignal line.

2. An equi-signal radio beacon aerial system comprising three directional aerials having their axes of maximum radiation parallel to the equisignal line, means for energizing said aerials, the outer of said aerials being set back with respect to the central aerial so that lines drawn through similar portionsvof each outer and the central aerial make acute angles with the equi-signal line so that a resultant radiation pattern is produced on each side of said line having an axis of maximum radiation which is divergent from said equi-signal line.

3. An equi-signal radio beacon aerial system comprising four directional aerials having their axes of maximum radiationl parallel to the equisignal line and positioned symmetrically on either side of said line, means for energizing said aerials, the outer aerials being set back with respect to the central ones so that lines drawn through similar portions of each outer and the adjacent inner aerial make acute angles with the equi-signal line to produce a resultant radiation pattern on each side `of said line having axis of maximum radiation which is divergent from said equi-signal line.

4. An equi-signal radio beacon aerial system comprising four directional aerials having their axes of maximum radiation parallel to' the equisignal line and positioned symmetrically on either side of said line, means for energizing said aerials and phasing means for adjusting the phase of current in the outer of said aerials with respect to currents in respective inner aerials to produce a resultant radiation pattern on each side of said line whose axis of^"maximum radiation is divergent from said equi-signal line.

5. An equi-signalradio beacon aerial system comprising a pair of seriesphase aerials, one of said pair being positioned 'on each side of an equi-signal line., said aerials having their longitudinal axes parallel to saidline, other series phase radiating means intermediate said pair of aerials, a source of energizing currents,`means for applying said energizing currents alternately to ldifferent ones of said pair of aerials and means for applying-said energizing currents to said intermediate radiating means so that standing waves are produced on saidpair of aerials and said. intermediate radiating means, and means for displacing the standing waves on said intermediate radiating mean's with respect to the standing waves on Said pair of aerials so that the resultant directions of maximum radiation are at an angle to said line.

JOHN MEGARRY FURNIVAL.

BERTRAM JOHN WITT.

CHRISTOPHER SYDNEY COCKERELL. 

